They are tiny bodies of varying shape(cylindrical,rod-like,spherical)distributed in cytoplasm. Each mitochondria is surrounded by double membrane.Outer membrane is porous.Inner membrane has folds and therefore have large surface area.These folds are called cristae and contain small rounded bodies called F1 particles or oxysomes.

The interior cavity of mitochondria is filled with gel like matrix which contain few small size ribosomes,circular DNA,phosphate granules.

Function 1)They are sites of cellular respiration. 2)They uses oxygen to oxidise carbohydrates and fats present in the cell to carbon dioxide and water.Oxidation releases energy,a portion of which is used to form ATP. Since mitochondria synthesises energy rich compound ATP it is called powerhouse of cell. ATP is called energy carrier or energy currency of the cell. 3)Mitochondria are able to make some of their own proteins,so they are regarded as semiautonomous organelles.